A possible role of linked Na and Cl movement in active Cl uptake in smooth muscle.

Smooth muscles actively accumulate Cl. Abolition of the transmembrane Na gradient has been shown to lead to a passive distribution of Cl. This suggested to us that Na and Cl may move together across the smooth muscle cell membrane, Cl accumulation resulting due to [Na]i being less than [Na]o. In favour of this view are the findings that Cl uptake is reduced in Na-free medium, Na uptake is reduced in Cl-free medium, reducing [Cl]i reduces Na efflux, and increasing [Na]i increases Cl efflux.